Changes in the architecture of fluvial deposits in the Paganzo Basin (Upper Paleozoic of San Juan province) : an example of sea level and climatic controls on the development of coastal fluvial environments

Paganzo Group exposures (Tupe Formation) in the Huaco area provide an excellent opportunity for assessing the role of sea level and climatic changes on the morphology and nature of coastal fluvial systems deposited in areas of limited tectonic activity. The paleogeographic position of Huaco, close to a coastal region within the Paganzo Basin, allows identification of the effects of sea level change on fluvial architecture. Despite the fact that the Huaco area was dominated by coastal fluvial systems, three marine incursions flooded this part of the basin during the Namurian, Early Pennsylvanian and Late Pennsylvanian respectively. During deposition of the Paganzo Group, climatic conditions evolved from glacial (Namurian) to hot and dry (Late Cisuralian). Five types of fluvial deposits were recognized on the basis of architectural element analysis, lithofacies distribution and type of fluvial bounding surfaces present. Fluvial system 1 (FS1) constitutes the lower part of the Tupe Formation and consists of stacked multi-storey channel-fill complexes formed on large braided alluvial plains dominated by channel-avulsion processes. FS2 consists of multi-storey channels alternating with floodplain deposits including coal beds and organic-rich mudstones. This fluvial system is interpreted as the deposit of an anastomosed network of sandy channels. FS3 occurs between the Early Pennsylvanian and Late Pennsylvanian marine transgressions and consists of sandstones and some conglomerates that form stacked channel complexes. Sporadically, very fine-grained sandstone and mudstone floodplain deposits appear as thin intercalations. FS3 likely formed on braided alluvial plains with channels dominated by transversal bars. FS 4 corresponds to an anastomosed fluvial system that was dominated by two types of braided channel belts that were separated by narrow floodplains. Finally, FS5 is composed of fining-upward cycles ranging from gravely sandstones at the bottom of channels to muddy floodplain deposits at the top. The whole FS5 succession was deposited by high-sinuosity meandering rivers. Detailed stratigraphic analyses clearly suggest that both, sea level and climate changes were first-order controls on fluvial system configurations. In this way, braided systems belonging to FS1 correspond to a low-accommodation system tract. Whereas, coal beds of FS2, which resulted from high water-tables, correspond to a high accommodation system tract that was likely associated with advanced stages of the Late Pennsylvanian transgression. A significant change in the nature of fluvial deposits took place prior to the Late Pennsylvanian sea level rise when braided fluvial systems (FS3) with very scarce floodplain deposits prevailed. Towards the top of the Late Pennsylvanian transgressive deposits, a high relief fluvial incision surface was carved into the underlying marine deposits. This surface was later mantled by anastomosed rivers (FS4) corresponding to low-accommodation deposits formed in a lowstand or during the early stages of the ensuing sea level rise. In later phases of this transgression, high accommodation conditions prevailed and fluvial sedimentation was dominated by high-sinuosity rivers (FS5). These fluvial deposits are considered as an inland equivalent to the shallow-marine deposits exposed in the neighboring Agua Negra Formation located to the west

Emission of monoterpenes from European beech (<i>Fagus</i><i> sylvatica</i> L.) as a function of light and temperature

International audienceUsing a dynamic branch enclosure technique European beech (Fagus sylvatica L.) was characterised as a strong emitter of monoterpenes, with sabinene being the predominant compound released. Since monoterpene emission was demonstrated to be a function of light and temperature, application of light and temperature dependent algorithms resulted in reasonable agreement with the measured data. Furthermore, during high temperature periods the depression of net CO2 exchange during midday (midday depression) was accompanied by a depression of monoterpene emission on one occasion. The species dependent standard emission factor and the light and temperature regulated release of monoterpenes is of crucial importance for European VOC emissions. All measurements were performed within the framework of the ECHO project (Emission and CHemical transformation of biogenic volatile Organic compounds) during two intensive field campaigns in the summers of 2002 and 2003

Estimations of isoprenoid emission capacity from enclosure studies: measurements, data processing, quality and standardized measurement protocols

The capacity for volatile isoprenoid production under standardized environmental conditions at a certain time (ES, the emission factor) is a key characteristic in constructing isoprenoid emission inventories. However, there is large variation in published ES estimates for any given species partly driven by dynamic modifications in ES due to acclimation and stress responses. Here we review additional sources of variation in ES estimates that are due to measurement and analytical techniques and calculation and averaging procedures, and demonstrate that estimations of ES critically depend on applied experimental protocols and on data processing and reporting. A great variety of experimental setups has been used in the past, contributing to study-to-study variations in ES estimates. We suggest that past experimental data should be distributed into broad quality classes depending on whether the data can or cannot be considered quantitative based on rigorous experimental standards. Apart from analytical issues, the accuracy of ES values is strongly driven by extrapolation and integration errors introduced during data processing. Additional sources of error, especially in meta-database construction, can further arise from inconsistent use of units and expression bases of ES. We propose a standardized experimental protocol for BVOC estimations and highlight basic meta-information that we strongly recommend to report with any ES measurement. We conclude that standardization of experimental and calculation protocols and critical examination of past reports is essential for development of accurate emission factor databases.JRC.H.7-Climate Risk Managemen

Paleoenvironments and age of the Talampaya Formation: The Permo-Triassic boundary in northwestern Argentina

© 2015 Elsevier Ltd. The Talampaya Formation is the basal unit of the Ischigualasto-Villa Unión rift system and has been traditionally assigned to the Triassic based on stratigraphic relationships. A median U-Pb age of 252.38 (+0.09/-0.22) Ma was obtained from volcanic zircons collected from a tuff bed close to the top of this unit at the Bordo Atravesado locality in the Cuesta de Miranda area (La Rioja, Argentina). This radiometric age is very close to the accepted Permian-Triassic boundary indicating that, at least in this locality, sedimentation occurred during the Late Permian but may have extended into the earliest Triassic. This new evidence indicates that the onset of the extensional event that gave rise to the rift basins in western Argentina started during the Permian. Detailed sedimentological studies of the 260 m thick Talampaya Formation allowed subdividing the succession into seven facies associations grouped into three evolutionary stages indicating that sedimentary environments initially evolved from alluvial fans to a braided river system. Subsequent intrabasinal volcanism associated with sediment deposition by low-to moderate-sinuosity rivers is recorded in the lower third of the column. The middle and upper part of the unit captures the evolution from ephemeral fluvial systems with an eolian interval to an ephemeral clastic lake with intermittent volcanic ash deposits. These changes indicate a progressive lowering of the landscape and a transition towards arid or semiarid conditions

Isoprene and monoterpene fluxes from central amazonian rainforest inferred from tower-based and airborne measurements, and implications on the atmospheric chemistry and the local carbon budget

We estimated the isoprene and monoterpene source strengths of a pristine tropical forest north of Manaus in the central Amazon Basin using three different micrometeorological flux measurement approaches. During the early dry season campaign of the Cooperative LBA Airborne Regional Experiment (LBA-CLAIRE-2001), a tower-based surface layer gradient (SLG) technique was applied simultaneously with a relaxed eddy accumulation (REA) system. Airborne measurements of vertical profiles within and above the convective boundary layer (CBL) were used to estimate fluxes on a landscape scale by application of the mixed layer gradient (MLG) technique. The mean daytime fluxes of organic carbon measured by REA were 2.1 mg C m^−2 h^−1 for isoprene, 0.20 mg C m^−2 h^−1 for α-pinene, and 0.39 mg C m^−2 h^−1 for the sum of monoterpenes. These values are in reasonable agreement with fluxes determined with the SLG approach, which exhibited a higher scatter, as expected for the complex terrain investigated. The observed VOC fluxes are in good agreement with simulations using a single-column chemistry and climate model (SCM).\ud \ud In contrast, the model-derived mixing ratios of VOCs were by far higher than observed, indicating that chemical processes may not be adequately represented in the model. The observed vertical gradients of isoprene and its primary degradation products methyl vinyl ketone (MVK) and methacrolein (MACR) suggest that the oxidation capacity in the tropical CBL is much higher than previously assumed. A simple chemical kinetics model was used to infer OH radical concentrations from the vertical gradients of (MVK+MACR)/isoprene. The estimated range of OH concentrations during the daytime was 3–8×10^6 molecules cm^−3, i.e., an order of magnitude higher than is estimated for the tropical CBL by current state-of-the-art atmospheric chemistry and transport models. The remarkably high OH concentrations were also supported by results of a simple budget analysis, based on the flux-to-lifetime relationship of isoprene within the CBL. Furthermore, VOC fluxes determined with the airborne MLG approach were only in reasonable agreement with those of the tower-based REA and SLG approaches after correction for chemical decay by OH radicals, applying a best estimate OH concentration of 5.5×10^6 molecules cm^−3. The SCM model calculations support relatively high OH concentration estimates after specifically being constrained by the mixing ratios of chemical constituents observed during the campaign.\ud \ud The relevance of the VOC fluxes for the local carbon budget of the tropical rainforest site during the measurements campaign was assessed by comparison with the concurrent CO2 fluxes, estimated by three different methods (eddy correlation, Lagrangian dispersion, and mass budget approach). Depending on the CO2 flux estimate, 1–6% or more of the carbon gained by net ecosystem productivity appeared to be re-emitted through VOC emissions

Significant light and temperature dependent monoterpene emissions from European beech (fagus sylvatiga L.) and their potential impact on the European VOC budget

By using a dynamic branch enclosure system the emission of monoterpenes from European beech (Fagus sylvatica L.) was investigated during two consecutive summer vegetation periods in the years of 2002 and 2003 in Germany. All measurements were performed under field conditions within the framework of the ECHO project (Emission and Chemical Transformation of Biogenic Volatile Organic Compounds, AFO 2000). European beech was characterized as a substantial emitter of monoterpenes, with sabinene being the predominant compound released. The monoterpene emission from European beech was shown to be a function of light and temperature and agreed well to emission algorithms that consider a light and temperature dependent release of volatile organics. Standard emission factors that were measured from these sunlit leaves of European beech ranged up to 4–13 µg g-1 h-1 (normalized to 1000 µmol m-2 s-1, 30°C) in the years of 2003 and 2002, respectively. The nighttime emission of monoterpene compounds was negligible. Also the artificial darkening of the sunlit branch during daylight conditions led to an immediate cessation of monoterpene emission. European beech is the dominating deciduous tree species in Europe. To demonstrate the effect of an updated monoterpene emission factor for European beech in combination with the consideration of a light and temperature dependent monoterpene emission, we applied a species based model simulation on a European scale. With respect to conventional estimates of the European volatile organic compound budget, the latter simulation resulted in relative increases of 16% by taking solely this tree species into account. On local scales these increases exceeded even more than 100% depending on the respective vegetation area coverage of European beec

Climatic Feedbacks and Desertification: The Mediterranean Model

Abstract Mesometeorological information obtained in several research projects in southern Europe has been used to analyze perceived changes in the western Mediterranean summer storm regime. A procedure was developed to disaggregate daily precipitation data into three main components: frontal precipitation, summer storms, and Mediterranean cyclogenesis. Working hypotheses were derived on the likely processes involved. The results indicate that the precipitation regime in this Mediterranean region is very sensitive to variations in surface airmass temperature and moisture. Land-use perturbations that accumulated over historical time and greatly accelerated in the last 30 yr may have induced changes from an open, monsoon-type regime with frequent summer storms over the mountains inland to one dominated by closed vertical recirculations where feedback mechanisms favor the loss of storms over the coastal mountains and additional heating of the sea surface temperature during summer. This, in turn, favors Mediterranean cyclogenesis and torrential rains in autumn–winter. Because these intense rains and floods can occur anywhere in the basin, perturbations to the hydrological cycle in any part of the basin can propagate to the whole basin and adjacent regions. Furthermore, present levels of air pollutants can produce greenhouse heating, amplifying the perturbations and pushing the system over critical threshold levels. The questions raised are relevant for the new European Union (EU) water policies in southern Europe and for other regions dominated by monsoon-type weather systems